In a study conducted between late 2024 and early 2026, researchers surveying southern California garden stores discovered the invasive Thrips parvispinus hiding on ornamental plants, showing the pest may be more widespread than previously reported and highlighting the need for vigilant monitoring to prevent its further spread. (Photo by F. LaBry via iNaturalist, CC BY 4.0)

By Andrew Porterfield

The tiny invasive Thrips parvispinus can cause considerable damage to peppers and ornamental plants, posing a serious economic threat. Originally from southeast Asia, the thrips species has spent the last century spreading to Australia, Europe, and North America.

Specifically in North America, it is established in Hawaii, Florida, and Ontario and has been detected in Colorado, North Carolina, South Carolina, Georgia, and Texas.

Its biology is not well known, making detection and management a serious challenge. Thrips parvispinus is known to feed on a large number of plant species, but pest managers have noted severe damage most often occurs on Capsicum, Mandevilla, Dipladenia, and Gardenia plants. Few insecticides are effective in controlling thrips, and those that are effective need frequent applications that drive up management costs and increase risks of the insects developing resistance. This means that early detection is for now the best way to control thrips damage.

In a study conducted between late 2024 and early 2026, researchers surveying southern California garden stores discovered the invasive Thrips parvispinus hiding on ornamental plants, showing the pest may be more widespread than previously reported and highlighting the need for vigilant monitoring to prevent its further spread. (Photo by F. LaBry via iNaturalist, CC BY 4.0)

Andrew Porterfield

In their search for better detection methods, a research team led by Eric Middleton, Ph.D., area IPM advisor at the University of California Division of Agriculture and Natural Resources in San Diego, surveyed retail garden stores in San Diego and Orange counties—known for their mild climate that would encourage insect growth—to see if they could uncover thrips hidden in plants. Their results, published in September in the open-access Journal of Insect Science, show that they could indeed find Thrips parvispinus in plants sold by retail garden stores in southern California, even though the species had not been officially reported there yet.

The team surveyed 30 retail garden stores in the two counties, taking four rounds of samples between November 2024 and January 2026. They used tap sampling that collected insects for later identification; any thrips seen in flowers were collected with a fine paintbrush. They started finding thrips at the very first store they surveyed, which was a surprise to Middleton. “At the very first store we sampled, and the very first host plant we sampled, we found T. parvispinus,” Middleton says. “The entire project was speculative at the beginning … so it was very validating—and worrisome—to immediately find a damaging insect pest the moment we start looking for it.”

In a study conducted between late 2024 and early 2026, researchers surveying southern California garden stores discovered the invasive Thrips parvispinus hiding on ornamental plants. Most thrips are about 1 millimeter in length, making them easy to miss and tricky to collect. Here, Eric Middleton, Ph.D., of the University of California Division of Agriculture and Natural Resources in San Diego, collects thrips with a fine paintbrush. “At the very first store we sampled, and the very first host plant we sampled, we found T. parvispinus,” Middleton says. (Photo by Eric Middleton, Ph.D.)

In a study conducted between late 2024 and early 2026, researchers surveying southern California garden stores discovered the invasive Thrips parvispinus hiding on ornamental plants. Most thrips are about 1 millimeter in length, making them easy to miss and tricky to collect. Here, Eric Middleton, Ph.D., of the University of California Division of Agriculture and Natural Resources in San Diego, collects thrips with a fine paintbrush. “At the very first store we sampled, and the very first host plant we sampled, we found T. parvispinus,” Middleton says. (Photo by Eric Middleton, Ph.D.)

In fact, the team found thrips and thrips feeding damage on all host plant types in 22 of 27 San Diego County stores and two of three Orange County stores. After reporting their findings to county regulators and store managers, the second and third round of surveys showed no thrips, but the final round showed the insect had reappeared in stores, in greater abundance than before.

Thrips cause damage when larvae and adults feed by piercing plant tissue epidermal layers and eating the cell contents. This creates the feeding scars, bronzed leaves, distorted growth, flower drop, and scarred fruit that growers see. Also, thrips are not easy to find and can complete their entire life cycle in two weeks, allowing new populations to quickly build up.

For those reasons, “normal inspection methods” by regulators often overlook thrips. These methods “usually involve inspectors visually checking a subset of plants that are imported into the area,” Middleton says. “Thrips parvispinus is hard to stop, and even on plants with clear damage symptoms you often won’t see the thrips at all. This is a very tricky pest to contain, and there is a reason it has been spreading across the U.S. pretty rapidly in the past few years.”

In a study conducted between late 2024 and early 2026, researchers surveying southern California garden stores discovered the invasive Thrips parvispinus hiding on ornamental plants, showing the pest may be more widespread than previously reported and highlighting the need for vigilant monitoring to prevent its further spread. (Photo by Eric Middleton, Ph.D.)

As for why the thrips reappeared after apparently disappearing from the garden stores, Middleton suggests that new plants keep arriving, carrying the thrips with them. “Even if we successfully stop one infestation at a nursery supplying these stores, the thrips can pop up again if the main nursery isn’t constantly monitoring incoming plants and trying to suppress populations,” he says. His team has recently begun a fifth round of sampling the garden stores, and preliminary results indicate even greater numbers of T. parvispinus than any of the earlier rounds.

The most important steps growers, inspectors, and consumers can take is aggressive monitoring of plants. “If growers, inspectors, and pest control advisors all know what to look for and do so regularly and diligently, it will certain help reduce the ability of T. parvispinus to spread undetected.”

Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He is based in Camarillo, California. Connect with him via LinkedIn or via email at [email protected].